The present invention relates generally to devices and methods for monitoring the presence or concentrations of additives to natural or industrial water systems. More specifically, the present invention relates to a modular fluorometer, which can be used to detect one or more fluorophores in water from a natural or an industrial water system.
The use of fluorophores in industrial water systems or in hydrology in general is known. The use of inert fluorescent tracers for determining the hydraulic losses in an industrial water system is known. Furthermore, using fluorescent tracers for controlling additive or product dosage to a recirculating or once-through cooling water system is also known (see U.S. Pat. No. 4,783,314). In this method, a fluorescent tracer is combined with one or more additives in a known proportion of tracer to additive(s) and then the mixture is added to the water of a cooling system. A fluorometer is then used to detect the presence and concentration of the fluorescent tracer in the cooling water and therefore the presence and concentration of the amount of additive.
A fluorometer is an analytical device that essentially comprises a light source, a means of selecting the desired excitation wavelength range, a sample cell, a means of selecting the desired emission wavelength range, and a detector. A spectrofluorometer is a specific type of fluorometer where the means for selecting the excitation and/or emission wavelength range is performed by a grating. A grating acts to disperse a continuum of light into its components. Spectrofluorometers may be further subdivided into scanning spectrofluorometers, those that use a mechanical means to scan the wavelength spectrum based on the position of the grating relative to the excitation source and/or emission (this describes a standard laboratory model fluorometer), or fixed spectrofluorometers where the grating is fixed with respect the emission. The emission (fluorescence) is then directed to an array of detectors. The array of detectors could be charge coupled devices, usually abbreviated xe2x80x9cCCDxe2x80x9d or the array of detectors could be photodiodes. The detectors are then calibrated in the appropriate wavelength units. A commercial device such as this is available from Ocean Optics (available from Drysdale and Associates, Inc., P.O. Box 44055, Cincinnati, Ohio 45244 (513) 831-9625). This type of fixed spectrofluorometer still requires the appropriate excitation wavelength selection device, which could be a scanning grating or filter.
The fluorometers that are most suitable for use under field conditions are not grating spectrofluorometers, rather, they are filter-based fluorometers. A filter-based fluorometer uses a filter to exclude all but the selected wavelength range. Most currently available filter-based fluorometers have one channel with this channel containing an optically appropriate cell.
A light source and an optional excitation filter, are positioned on one side of the optically appropriate cell and an emission detector, and an emission filter are positioned on the opposite side of the optically appropriate cell. A reference detector may optionally be present. Because fluorescence is isotropic, most fluorometers detect any fluorescent light emitted from the fluorophore at a 90xc2x0 angle from the light source in order to minimize collection of any spurious excitation light.
The excitation filter permits light of the chosen excitation wavelength range to pass through the filter and into the cell. When conducting off-line batch testing, a sample of water, from a natural or an industrial water system, is placed and held in the optically appropriate cell. When conducting on-line testing the sample of water flows through the optically appropriate cell. The light is absorbed by the fluorophore present in the water sample, which, in turn, emits a fluorescent light (hereinafter known as a fluorescent signal) having the same or a longer wavelength than the excitation light. The emission filter, which is positioned between the emission detector and the optically appropriate cell, is chosen so as to permit only the light emitted by the fluorophore (the fluorescent signal of the fluorophore) to pass through the filter to the emission detector.
A limitation of currently available filter-based fluorometers is that most of them are capable of detecting only a single fluorophore species. This is because the use of a photodiode requires the use of an emission filter specifically designed to permit the passage of the fluorescent signal emitted by a single fluorophore.
The detection of a plurality of fluorophore species can be important because it is often desirable to add a plurality of additives or chemicals or inert fluorescent tracers to an industrial water system.
Another reason for needing a fluorometer capable of measuring more than one fluorescent signal is that certain fluorescent signals emitted by certain non-inert fluorophores are designed to change in response to interactions with other components of an industrial water system. Therefore, an analysis of the different fluorescent signals emitted by a single fluorophore would require the use of a plurality of currently known fluorometers.
Using a plurality of currently known fluorometers is expensive and very often not a practical, field-acceptable solution to this problem. Several other practical solutions to this problem are described in the following text.
There are known fluorometers that are xe2x80x9cmultisignal-detector-one-channelxe2x80x9d fluorometers. These fluorometers have one channel with more than one set of light source/filter/detectors and thus are capable of measuring more than one fluorescent signal in a water sample. One such type of xe2x80x9cmultisignal-detector-one-channelxe2x80x9d fluorometer includes a photodiode array as opposed to an individual photodiode. The problem is that photodiode arrays are expensive and fragile when used in an industrial environment such as a cooling tower or boiler water system. Accordingly, many operators of industrial water systems are reluctant to employ such an expensive and fragile piece of equipment in a hostile environment. As a result, operators, in certain circumstances, have been forced to employ a number of different fluorometers for a single industrial water system. This method is disadvantageous due to the size, cost and bulk of the required fluorometers.
A specific type of multisignal-detector-one-channelxe2x80x9d fluorometer is described in xe2x80x9cImproved Multilaser/Multiparameter Flow Cytometer for Analysis and Sorting of Cells and Particles, by Steinkamp et al., Rev. Sci. Instrum. (1991), 62(11), 2751-64. The fluorometer described therein requires expensive and fragile components. Therefore, this fluorometer is not practical or suitable for field work.
The practical difficulty in using these available filter-based fluorometers is that they can only measure what they have been set up to measure and once the light source, detector and filters have been set up it takes time and effort to change any of these elements to make the fluorometer capable of measuring fluorescent signals at other wavelengths of light.
As a result of the perceived deficiencies in existing fluorometers, there exists a need for an improved fluorometer which is capable of detecting one or more fluorophores using a single apparatus, with the capability of rapidly changing the operating setup of the fluorometer so that the desired fluorescent signals can be detected. Still further, there is a need for a method for detecting one or more fluorophores in a system utilizing such a single fluorometer.
The first aspect of the instant claimed invention is a modular fluorometer comprising:
one or more units with each unit comprising:
a channel comprising an optically appropriate cell through which a water sample flows;
a light source positioned outside said optically appropriate cell;
an optional excitation filter positioned between the light source and the optically appropriate cell;
a reference detector positioned outside the optically appropriate cell;
an emission detector positioned outside the optically appropriate cell;
an optional emission filter positioned between said emission detector and said optically appropriate cell;
wherein if more than one unit is present in said modular fluorometer, said optically appropriate cells through which said water sample flows are aligned such that only one channel through which a water sample flows exists in said fluorometer.
The second aspect of the instant claimed invention is a method of detecting the presence of one or more fluorophore species in a water sample wherein each of said fluorophore species emit light of different emission spectra after being illuminated with light defined by different excitation spectra, the method comprising the steps of:
a) providing the modular fluorometer of the first aspect of the instant claimed invention, wherein said modular fluorometer has sufficient units to detect the presence of each fluorophore species in said water sample;
b) moving a water sample comprising the fluorophores through each respective optically appropriate cell;
c) illuminating said water sample with the respective light source in each unit;
d) detecting each fluorophore species by detecting the emission spectra with the respective emission detectors in each unit.
The third aspect of the instant claimed invention is a method of controlling an industrial water system comprising using the modular fluorometer of the first aspect of the instant claimed invention, wherein said modular fluorometer further comprises a controller with said controller comprising isolated analog inputs such that the controller is capable of using the measured fluorescent signals provided by the modular fluorometer and input from other analytical devices to control an industrial water system.